Monoclonal antibodies directed against the idiotype of the immunoglobulin expressed by the tumor cells of a given B cell lymphoma have been shown to have an exciting potential for therapeutic use. The proposed studies will seek to clarify the mechanisms and characteristics of anti-idiotype antibodies important for anti-tumor effects in a mouse B cell lymphoma model (38C-13). Our preliminary studies of this model indicate striking differences in therapeutic efficacy against tumor challenge among four recently produced monoclonal syngenenic anti-idiotype antibodies of three different isotypes. One of these antibodies is clearly superior to the others and is of the IgG2a isotype. To unambiguously determine if the isotype of these antibodies is critical for therapeutic effectiveness, we will isolate class switch variants occurring spontaneously in each of the original anti-idiotype hybridoma lines. Thus matched sets of antibodies identical in all respects to the parent hybridoma antibodies except for heavy chain subclass will be generated and compared in vivo and in vitro. By combining a sensitive radioimmunoassay for detection in culture supernatants of the desired isotype and a sequential culture sublining approach, we have successfully cloned one such class switch variant. Other characteristics of these antibodies will also be examined for their relative importance such as their affinity for the idiotype target, their ability to induce modulation of cell surface idiotype, and their epitopic specificity. Further investigations will concern the capacity of these antibodies to induce immunoregulatory mechanisms in the host which are dissociated from the direct binding of these antibodies to tumor cells (eg. induction of idiotype-anti-idiotype networks). Initial investigations of the latter will involve, for example, observing the effects of administering antibodies far enough in advance of tumor challenge so that these antibodies are no longer detectable when tumor cells are actually given. The results of the above studies should be instrumental in forming a basis for rational selection of antibodies for therapy in human B cell malignancy and in elucidating immunologic mechanisms involved in tumor rejection mediated by antibodies.